Is 512MB as opposed to 256MB in a video card very notable? In other words, is this what's new (just like how quadcore is the new talk of the town)? what does that little extra do for the overall display presentation? And also, my current MB houses the NVIDIA GeForce 9400M graphics. Is the new iMac's ATI Radeon HD 4670 graphics with 256MB & the ATI Radeon HD 4670 graphics with 256MB currently blowing my card away?